Tape storage system including multiple tape storage apparatuses

ABSTRACT

A tape storage system according to one embodiment includes two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, where a first of the tape storage apparatuses is configured to receive multiple data clusters and a synchronization request from a host, and, when one of the segments of the buffer is accumulated and filled with the data, to write the accumulated data onto a tape. A second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and being configured to write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

RELATED APPLICATIONS

This application claims priority to PCT Patent Appl. No. PCT/JP2010/060111, filed Jun. 15, 2010, and which is herein incorporated by reference.

BACKGROUND

The present invention relates to a tape recording system including multiple tape storage apparatuses, which improves writing performance in the case of a host requesting writing of multiple data clusters and frequently providing synchronization requests.

When a tape storage apparatus (hereinafter also referred to as a tape drive or a drive) writes data to a tape medium (hereinafter, a tape or a tape medium), the drive does not typically immediately write the data sent from a host. The drive stores the data into a buffer in the drive, and starts writing after a sufficient amount of data has been accumulated.

SUMMARY

A tape storage system according to one embodiment includes two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, wherein a first of the tape storage apparatuses is configured to receive multiple data clusters and a synchronization request from a host, and, when one of the segments of the buffer is accumulated and filled with the data, to write the accumulated data onto a tape; and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters via the first tape storage apparatus, and the second tape storage apparatus being configured to write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

A tape storage system according to another embodiment includes two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, a first of the tape storage apparatuses being configured to receive multiple data clusters and a synchronization request, e.g., sent from a host, and being configured to write a predetermined number of data clusters accumulated in the segments onto a tape at a timing corresponding to the synchronization request, and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters, e.g., sent from the host via the first tape storage apparatus, and, when the segment thereof is accumulated and filled with the data, writing the accumulated data onto a second tape.

A method according to yet another embodiment, in a first tape storage apparatus having a buffer divided in fixed-length segments, receiving multiple data clusters and a synchronization request, e.g., from a host, and, when one of the segments of the buffer is accumulated and filled with the data, writing the accumulated data onto a tape; and in a second tape storage apparatus having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, receiving the multiple data clusters via the first tape storage apparatus, and writing a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

A computer program product according to one embodiment includes a computer readable storage medium having computer readable program code embodied therewith. The computer readable program code includes: computer readable program code configured to cause a first tape storage apparatus having a buffer divided in fixed-length segments to receive multiple data clusters and a synchronization request, and, when one of the segments of the buffer is accumulated and filled with the data, write the accumulated data onto a tape; and computer readable program code configured to cause a second tape storage apparatus, having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, to receive the multiple data clusters via the first tape storage apparatus, and write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

Other aspects and embodiments of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts the correspondence between a buffer and written data (data sets) on a tape according to one embodiment.

FIG. 2 shows a configuration diagram of a tape drive according to one embodiment.

FIG. 3 shows a conceptual diagram of an RABF writing system according to one embodiment.

FIG. 4 shows a time chart of BFWrite and ReWrite at the time of performing RABF writing according to one embodiment.

FIG. 5 shows a writing process of a first embodiment.

FIG. 6 shows a writing process of a second embodiment.

FIG. 7 shows a particular embodiment in which two hosts and three drives exist.

FIG. 8 shows an example of a procedure for a tape drive to switch among the works of a BF drive, an R drive and an regular drive functioning alone according to situations, as a fourth embodiment according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.

The following description discloses several preferred embodiments of tape storage systems. These embodiments are presented by way of example only and are not intended to limit the present invention to only the embodiments explicitly disclosed.

In one general embodiment, a tape storage system includes two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, wherein a first of the tape storage apparatuses is configured to receive multiple data clusters and a synchronization request from a host, and, when one of the segments of the buffer is accumulated and filled with the data, to write the accumulated data onto a tape; and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and the second tape storage apparatus being configured to write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

In another general embodiment, a tape storage system includes two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, a first of the tape storage apparatuses being configured to receive multiple data clusters and a synchronization request sent from a host, and being configured to write a predetermined number of data clusters accumulated in the segments onto a tape at a timing corresponding to the synchronization request, and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and, when the segment thereof is accumulated and filled with the data, writing the accumulated data onto a second tape.

In another general embodiment, a method includes, in a first tape storage apparatus having a buffer divided in fixed-length segments, receiving multiple data clusters and a synchronization request, e.g., from a host, and, when one of the segments of the buffer is accumulated and filled with the data, writing the accumulated data onto a tape; and in a second tape storage apparatus having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, receiving the multiple data clusters via the first tape storage apparatus, and writing a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

In another general embodiment, a computer program product includes a computer readable storage medium having computer readable program code embodied therewith. The computer readable program code includes: computer readable program code configured to cause a first tape storage apparatus having a buffer divided in fixed-length segments to receive multiple data clusters and a synchronization request, and, when one of the segments of the buffer is accumulated and filled with the data, write the accumulated data onto a tape; and computer readable program code configured to cause a second tape storage apparatus, having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, to receive the multiple data clusters via the first tape storage apparatus, and write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.

FIG. 1 shows correspondence between a buffer and written data (data sets) on a tape. A buffer 120 is in the form of a ring divided in fixed-length segments 20. Multiple variable-length data clusters 10 sent from a host are sequentially accumulated in a segment 20. When the segment 20 is completely filled with data, a head 50 writes the contents onto a tape 30 as a data set 40.

When all the data has been written onto the tape, and the segments of the buffer 120 become empty, the writing ends. When the writing is complete, the drive rewinds the tape in preparation for the next writing process. The position of the writing magnetic head of the drive is aligned with the position of the data end on the tape. This operation is called backhitch.

It takes about five seconds for one backhitch. It is desirable that the drive continues writing without backhitch whenever possible, thereby improving writing performance. In regular writing, the writing is performed while data is accumulated in the segments of the buffer 120 in the drive. The data clusters 10 are sequentially stored into the buffer 120 from the host over time, and sequentially written onto the tape as a data set when a segment is filled with the data. In regular writing from the host, since data is continuously sent, it is less likely that the buffer is completely emptied during the writing, and backhitch seldom occurs.

The host sometimes dumps all the data in the buffer onto the tape; that is, the host provides a synchronization request (Flush). The synchronization request is issued to confirm that the data temporarily stored in the buffer 120 has been written onto the tape. When the drive performs writing by flush, the buffer becomes empty of data, and therefore, a backhitch occurs. When the synchronization request is issued frequently, the number of backhitches increases, and the writing performance is deteriorated.

In order to prevent performance deterioration, a tape drive can perform writing without backhitch in response to a synchronization request for data stored in the buffer. This writing method is referred to as a backhitchless flush. In this writing method, since data is written onto a tape with data sets largely spaced apart from each other, the recording density of the tape is undesirably decreased.

In a proposed method to avoid such backhitch between synchronization requests, tape drives may implement a function called Recursive Accumulating Backhitchless Flush (RABF) which will be further discussed below. Backhitchless Flush (BF) is meant to be interpreted as writing which does not cause a backhitch operation. In writing with the RABF system, a tape drive can avoid time loss due to backhitches and a decrease in recording density for each synchronization request.

With this function, if a host frequently requests synchronization (Flush), data can be written into a track area, e.g. an Accumulate Backhitchless Flush area (ABF area), etc. different from a regular track area usually used for writing arbitrary variable-length data, without backhitch. Hereinafter, this writing function will be called Backhitchless Flush Write (BFWrite).

After a certain amount of data is written, the data is rewritten into the regular area where the data should be written. This writing is called Recursive Write (ReWrite). In this RABF operation, it is not necessary to wait for a succeeding series of data clusters to come from the host, backhitch does not intervene, and deterioration of writing performance is reduced. Furthermore, since a succeeding data set can be written immediately after a data set recorded on a tape, decrease in recording density can be avoided. However, it has been discovered that RABF functions have the following problem. BFWrite and ReWrite are alternately performed by one drive. Therefore, the regular track area and the ABF area are revisited frequently, and much time is required for the movement. Furthermore, since the same data is written twice both into the regular track area and the ABF area, extra time is required.

To alleviate such problems, one embodiment of the present invention provides a tape storage apparatus system which includes multiple tape storage apparatuses.

Furthermore, one embodiment may provide a tape recording system which, if a data writing error occurs in one tape drive, is able to restore the data.

A preferred embodiment of a tape storage system includes two or more tape storage apparatuses, each of which may have a tape mounted thereon and is provided with a buffer divided in fixed-length segments, and being connectable to a host that sends multiple data clusters (e.g., data strings, files, sets of data packets, etc.) and a synchronization request at a predetermined frequency (timing) to the tape storage apparatuses. The illustrative tape recording system may include a first tape storage apparatus connected to the host. The first tape storage apparatus is configured to receive the multiple data clusters sent from the host, and, when the segment of the buffer is accumulated (prepared) and filled with data, write the accumulated data onto a tape. A second tape storage apparatus is connected to the first tape storage apparatus, and is configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and dump a predetermined number of data clusters accumulated in the segments onto a tape at a timing corresponding to the synchronization request, e.g., as dictated in the synchronization request, upon receiving the synchronization request, etc.

According to one embodiment of the tape recording system, the first tape storage apparatus may not write data in the buffer until at least one segment of the buffer is completely accumulated with data, ignoring the synchronization request corresponding to the data; and when the predetermined number of data clusters accumulated in the segments of the buffer is to be dumped onto a tape at the timing corresponding to the synchronization request, the second tape storage apparatus pads (fills) an area of the segments which is unfilled with the data because the segments are not completely accumulated with the data, to write out all the data of the segments.

In another embodiment, a tape storage system includes two or more tape storage apparatuses, each of which may have a tape mounted thereon and is provided with a buffer divided in fixed-length segments, and being connectable to a host that sends multiple data clusters and a synchronization request at a predetermined frequency (timing) to the tape storage apparatuses. The tape recording system may include: a first tape storage apparatus connected to the host, and being configured to receive the multiple data clusters sent from the host, and to dump a predetermined number of data clusters accumulated in the segments onto a tape at a timing corresponding to the synchronization request; and a second tape storage apparatus connected to the first tape storage apparatus, receiving the multiple data clusters sent from the host via the first tape storage apparatus, and, when the segment is accumulated (prepared) and filled with the data, writing the accumulated data onto a tape.

According to the tape recording system of the one embodiment which is configured as described above and which includes at least two or more tape drives, there is obtained an advantageous effect of, for data writing from a host accompanied by frequent synchronization requests, improving writing performance and maintaining tape recording density.

In the present embodiment, two tape drives are used for the RABF function performed by one tape drive to omit writing by movement of a head accompanying the ReWrite operation. In one approach a tape storage system may include at least two tape drives. The tape recording system is connectable to a host. One drive performs ReWrite writing of the RABF function. This first drive is called an “R drive”. The other drive performs BF writing in response to a synchronization request from the host. This other drive is called a “BF drive”. Since these two function operations are performed by the two drives at the same time, writing performance is improved.

In one embodiment of the tape recording system, a tape on which writing has been performed by the first tape storage apparatus may be treated as a regular writing tape to which data accumulated in the segments of the buffer are written as data sets. On a tape on which writing has been performed by the second tape storage apparatus, data accumulated in the segments may be written as data sets, and the interval between the data sets on the tape reflects the time interval of the synchronization request.

In another approach of the tape recording system, the second tape storage apparatus is able to continuously and overwritably use an area of the second tape storing data already written by the first tape storage apparatus. For example, once the data is written to the tape by the first storage apparatus, any corresponding data on the second tape may be overwritten by the second tape storage apparatus.

With regard to driving of a tape storage apparatus (tape drive), FIG. 2 shows a configuration diagram of a tape drive 100. The tape drive 100 includes an interface 110, a buffer 120, a recording channel 130, a tape 14 a, a head 14 b, reels 14 c and 14 d, a cartridge 14 e having a cartridge memory (CM) 25, a motor 150, a controller 160, a head position control system 170 and a motor driver 185.

The interface 110 communicates with a host 105. The interface 110 receives a command instructing writing of data transferred to the buffer 120 and a command instructing writing of data in the buffer 120 to the tape 14 a, from the host 105. For example, the communication standard of the interface 110 may be SCSI or Fibre Channel. In the case of Fibre Channel, a request (command) to write to the buffer corresponds to Write. A synchronization request (command) to write out data existing in the buffer corresponds to WriteFM0.

As noted above, various embodiments have two or more tape storage apparatuses, which may each be a tape drive 100. Communication between the two tape drives may be via any suitable connection, such as an Ethernet connection.

The buffer 120 may be a memory for accumulating clusters of variable-length data 10 to be written onto the tape 14 a and may be Dynamic Random Access Memory (DRAM) or any other suitable memory. The buffer 120 may be separated in fixed-length segments 20, as shown in FIG. 1. The data cluster 10 with an arbitrary length is transferred from the host 105 to the drive.

The buffer 120 is called a ring buffer in the sense that it receives data up to the last segment and then starts to receive data from the first segment again. One segment 20 corresponds to one data set 40 of FIG. 1 on the tape 14 a or 30. One data set may be constituted by a part of one data cluster or multiple data clusters sent from the host 105.

The writing timing is when a segment is completely filled with data and when an area unfilled with data in a segment is filled by data padding in response to a synchronization request from the host. In this specification, these two cases in which a segment is filled with data may be expressed as a segment having been “prepared”.

With continued reference to FIG. 2, the tape 14 a is a tape medium useful for recording data. Data transferred via the recording channel 130 is written onto the tape 14 a by the head 14 b as a data set. The tape 14 a is wound around the reels 14 c and 14 d, and laterally moves from the reel 14 c toward the reel 14 d, or vice versa accompanying their rotation.

The cartridge 14 e may include a container for containing the reel 14 c around which the tape 14 a is wound. The same cartridge as the cartridge 14 e may be provided to contain the reel 14 d. The motor 150 rotates the reels 14 c and 14 d.

The tape cartridge 14 e is provided with a contactless non-volatile memory called a cartridge memory (CM) 25 therein. The tape drive 100 contactlessly reads from and writes to the CM 25. The tape drive updates tape directory information (attribute information about written data) in the CM. When reading data, the tape drive refers to the information included in the CM and moves the tape to a destination position at a high speed to enable alignment.

The controller 160 controls the whole tape drive 100. The controller 160 controls writing/reading of data to/from the tape 14 a in accordance with a command received by the interface 110 from the host 105. The controller also controls the head position control system 170 and the motor driver 185. The head position control system 170 traces a desired one or multiple wraps, or sets of multiple tracks. When it becomes necessary for the head 14 b to switch the track, the head position control system 170 performs control to electrically switch the head 14 b. The motor driver 185 may be directly connected to the controller 160.

If the next synchronization request is made without stopping the tape 14 a, there exists a wasteful long recording area between data written in response to the preceding synchronization request and data written in response to the next synchronization request. In order to reduce wasteful use of the recording capacity in a tape drive operation, it is necessary to minimize the interval between data sets written in the longitudinal direction of a tape medium.

During a backhitch operation, the tape medium 14 a is aligned with the head 14 b so that the next data is written immediately after a data set already written in the tape medium. Relative to the head 14 b, the tape 14 a reduces the traveling speed and stops once. After that, the tape medium is rewound to a position where writing is to be performed using the writing motor 150 for aligning the head with a tape position where the next data is to be written. About three to five second extra time is spent for this operation. If a synchronization request is issued from the host for each writing of multiple data clusters, the backhitch operation occurs frequently, and the performance of writing data transferred from the host is deteriorated. In some embodiments, tape drives are configured to use RABF in order to avoid such backhitches when writing is accompanied by a large number of synchronization requests.

FIG. 3 shows a conceptual diagram of the RABF writing system according to one embodiment. This is a method in which one tape drive performs writing by using a band of multiple tracks 145 as a temporary storage wrap 180 (ABF wrap) and a regular wrap 165 separately. One head has, for example, eight or sixteen writing/reading channels. A wrap is a collection of multiple, e.g., eight, sixteen, etc. tracks, and it is a unit of tracks which one head reads or writes at the same time. Data transferred from the host is written to the ABF wrap 180 (tracks 14 and 15) first without backhitch. Since the ABF wrap is an extended buffer for temporarily storing data at the time of writing the data to a tape, and the data is temporarily stored in the tape, it is possible to prevent disappearance of the data in the case of interruption of power supply and the like. The regular wrap 165 is constituted by tracks 1 through 13 to which data sets are written without wasting recording capacity. Upon receiving a synchronization request, the tape drive writes data in the buffer into the ABF wrap 180 without backhitch, while causing the tape medium to continue traveling. The data sets written in the ABF wrap are written back to the regular wrap 165, that is, a ReWrite is performed, via the buffer 120. The data sets (DS, DS+1, DS+2, etc.) are written at synchronization request intervals in a manner that data, indicated by being shaded, is newly and successively added to preceding data, also indicated by being shaded. The writing of these data sets is a buffer flash which is not accompanied by backhitch, also known as a Backhitchless Flush Write, or BFWrite, as noted above. An arrow for each data set indicates a pointer for the buffer being accessed by writing/reading control. The data sets DS+3, DS+7, DS+11, DS+15 and DS+19 correspond to data sets P1, P2, P3, P4 and P5 filled (prepared) with data. The operation of writing these prepared data sets P1, P2, P3, P4 and P5 to the regular wrap 165 (tracks 1, 2, 3, . . . , and 13) at a constant timing is recursively performed. This writing operation is called ReWrite. By the ReWrite operation, the data sets P1, P2, P3, P4 and P5 are completely filled (prepared) with data and written to the regular wrap 165 without wasting storage capacity. Since the tape drive adopting this RABF system does not have to perform a backhitch in response to synchronization requests issued frequently or continuously, improvement of the writing performance can be realized. One tape drive which has received multiple data clusters and a synchronization request performs the RABF function as the separate BFWrite and ReWrite functions.

Contribution to the whole writing performance, in the case where it is assumed that the ReWrite writing operation is omitted between the two operations, is examined. RABF writing is performed by the current tape drive, and processing time is measured. In the experiment, a process of making a synchronization request each time 1 MB of the amount of data of 680 MB was repeated, as an example of such a way of writing that RABF is effective. As temporary storage areas (ABF wraps), two adjoining wraps ABF1 and ABF2 are used. Writing/reading is performed for these two wraps in opposite directions. BFWrite is performed for these ABF areas. Next, ReWrite is performed for the regular wrap.

FIG. 4 shows a typical time chart of BFWrite and ReWrite at the time of performing RABF writing. Each event and wrap time thereof are shown below. The host makes a synchronization request each time 1 MB of data is transferred to a drive. Data (1 MB) sequentially sent are written to the wraps ABF1 and ABF2 by BFWrite without backhitch. In the experiment, when data corresponding to a data set is prepared, ReWrite of the data set to the regular wrap occurs frequently. Referring to FIG. 4 and the event time shown below, it is seen that ReWrite occupies more than 20 percent of the overall writing period.

Event Wrap time ABF1 BFWrite start 0 ABF2 BFWrite start 26.19 sec ReWrite start 50.65 sec ReWrite end 63.89 sec

About 63.89 seconds were required to write 680 MB using the RABF function in a single tape drive. The writing method corresponding to using two tape drives only took 50.65 seconds to write the same amount of data, because the time for ReWrite can be reduced. By performing a simple calculation (50.65/63.89)×100=79.27%, it is seen that the processing time can be reduced by more than 20 percent using two drives. This is an example of an illustrative case, and the processing time may be reduced more depending on the sequence. By allowing the ReWrite operation to be streamlined by using two tape drives, the writing performance is improved.

In one approach, one drive performs transmission/reception of data between the host and the drive. At the same time, two drives can perform transmission/reception of data between the drives by a communication function, for example, by Ethernet.

A BF drive may report completion of writing to the host. At the same time, it transmits data to the other R drive using inter-drive communication. The other R drive performs writing when sufficient data has been accumulated in the buffer 120 (FIG. 2) without depending on a synchronization request from the host.

In the case of a tape to which writing is performed by BFWrite without backhitch, writing is performed with a low recording density, and therefore, the tape consumption speed is high in comparison with a tape to which writing is performed with ReWrite. However, the ABF area of the tape to which BFWrite has been performed plays a role of a temporary cache until ReWrite is completed. Data in the ABF area for which ReWrite has been completed successfully may be overwritten. By using a tape used for the BF drive as an endless tape while overwriting data for which ReWrite writing has been completed, the tape used for the BF drive is never finished up.

Even if an error occurs at the time of writing data by the R drive and for which completion of writing has been reported, the data can be read out from the tape for which writing was performed by the BF drive. Because data for which writing has been completed by the BF drive can be restored by the tape in the other R drive, the situation in which the data cannot be read back can be avoided. Usually, a tape for which ReWrite has been performed is used at the time of reading the data out. Because the tape for ReWrite is a tape on which writing has been performed with a high density, the reading performance is also good.

In one embodiment of the system, if a data writing error occurs in the first tape storage apparatus, and the data has already been written by the second tape storage apparatus, the data writing error is not reported to the host.

In another embodiment of the system, if a data writing error occurs in the second tape storage apparatus, and the data has already been written by the first tape storage apparatus, the data writing error is not reported to the host.

In another embodiment of the system, if a data writing error occurs in the second tape storage apparatus, the data corresponding to the error may be written again into an unused tape area which includes a tape storage area of the second tape in the second tape storage apparatus that stores data already written in the first tape storage apparatus.

In still another approach of the system, if a data writing error occurs in the first tape storage apparatus, the data may be written from the second tape (e.g., a BF tape) in the second tape storage apparatus to restore data at an error position of the tape in the first tape storage apparatus via an inter-drive communication connection, such as those disclosed herein.

As for the positional relation between the host, and the BF and R drives, at least two kinds of methods may be used: a method in which the R drive is connected to the host and a method in which the BF drive is connected to the host. A processing procedure in each of the configurations is shown below. No matter which configuration writing is performed in, the same procedure for a reading process and procedure for a process performed at the time of occurrence of an error are used.

A first embodiment implements the method in which the R drive is directly connected to the host. The host makes a request to the R drive to mount a tape on which writing is to be performed. The R drive mounts an R tape and reports completion thereof to the host. The BF drives mounts a BF tape.

FIG. 5 shows a writing process of a first embodiment. The host HOST sends multiple variable-length data clusters to the tape recording system. The host sends a synchronization request to the data recording system immediately after particular data. By this synchronization request, the host can coordinate recording of multiple data clusters before the particular data, onto the tape. A tape for the R drive is called an “R tape” R TAPE. A tape for the BF drive is called a “BF tape” BF TAPE.

The host repeats writing (Write) of data to the R drive R DRIVE and a request of synchronization (Flush) thereof <1>. The R drive sequentially accumulates the data into the buffer BUFFER with data <2>. The BF drive also transmits each data cluster to the R drive R DRIVE using inter-drive communication and requests writing <3>. The image of the data written in tracks of the BF tape may be the same as the data sets (DS, DS+1, DS+2, etc.) sequentially written in the ABF wraps of the RABF technique shown in FIG. 3. Referring again to FIG. 5, each data set is written into a track of the BF tape in a backhitchless manner <4>.

The BF drive BF DRIVE makes a writing completion report to the R drive using inter-drive communication <5>. The R drive sends the writing completion report received from the BF drive, to the host <6>.

When one segment of the buffer is completely filled with multiple data clusters, the R drive writes the multiple data clusters of the segment to an R tape <7>. Finally, the R drive makes a writing completion report to the BF drive <8>.

In the continuous writing process described above, the BF drive treats a recording position on the BF tape having data which has already been written (recorded) on the R tape as overwritable free space.

Another embodiment may include a method in which the BF drive is directly connected to the host.

The host makes a request to mount a tape on which writing is to be performed, to the BF drive. The BF drive requests the R drive to mount an R tape using inter-drive communication. The BF drives itself mounts a BF tape. The R drive mounts the requested R tape and makes a completion report to the BF drive through inter-drive communication. The BF drive sends the mounting completion report from the R drive, to the host. Thereby, it appears to the host that the BF drive mounts the R tape, and the host recognizes that it is performing writing to the R tape.

FIG. 6 shows a writing process according to a second embodiment. The host HOST sends multiple variable-length data clusters to the tape recording system. The host sends a synchronization request to the data recording system immediately after particular data. By this synchronization request, the host can coordinate recording of multiple data clusters before the particular data, onto the tape.

The host repeats data writing (Write) to the BF drive BF DRIVE and requests a synchronization (Flush) thereof <1>. The BF drive immediately writes the data to a mounted BF tape BF TAPE even if a segment of its buffer is not filled <2>. The image of the data written in tracks of the BF tape may be the same as the data sets (DS, DS+1, DS+2, etc.) sequentially written in the ABF wraps of the RABF technique shown in FIG. 3. Each data set is written into a track of the BF tape without any backhitch.

With continued reference to FIG. 6, the BF drive then makes a writing completion report to the host <3>. Simultaneously with the process of step <3>, the BF drive transmits each data cluster to the R drive R DRIVE using inter-drive communication and requests writing <4>. The R drive sequentially accumulates each data cluster transmitted from the BF drive into the buffer BUFFER <5>.

When one segment of its buffer is filled with data and a data set is prepared, the R drive writes the data to an R tape R TAPE <6>. Finally, the R drive makes a writing completion report to the BF drive <7>.

In the continuous writing process described above, the BF drive treats a recording position on the BF tape having data which has already been written (recorded) on the R tape of the R drive is recorded as overwritable free space.

A reading method may be common to the first and second embodiments. No matter which configuration writing is performed in, the host recognizes that it has written data onto an R tape. Therefore, at the time of reading, reading from the R tape may be requested.

A process performed at the time of a writing error may be common to the first and second embodiments. Such process may be used whether an error occurs in the BF drive or the R drive at the time of writing. In the tape storage system of the first and second embodiments, it is not necessary to report the error to the host if writing of the relevant data has been successful in the other drive.

The BF drive rewrites the data in which an error has occurred, to another position on the tape. There is a high possibility that a writing error can be avoided or alleviated by changing the writing position on a tape. As the position to start the rewriting, the top of the tape may be used. However, in the case of the BF drive, it is preferable to avoid overwriting an area of data on a BF tape which the R drive has not been completed writing. This is because, if writing by the R drive fails, the data cannot be restored on a BF tape. The system should also avoid disappearance of data at the R drive when performing error processing at the time of writing onto a BF tape. The period during which data may disappear corresponds to a period during which, though data exists in the buffer of the R drive, writing of the data to a tape has not been completed.

Even when movement to a rewriting position is performed in the BF drive, the R drive can continue writing. Even when rewriting is performed in the BF drive, and the writing is not successful, it is not necessary to make an error report if the relevant data can be written by the R drive. Since an R tape is used at the time of reading, it is not necessary to be aware of an error on a BF tape.

If a writing error occurs in the R drive, the R drive records the position where the error has occurred, onto the non-volatile memory (CM) 25 (FIG. 2) mounted on the cartridge. In order to prevent overwriting of the data, the BF drive stores the range of the data that could not be written by the R drive, in the CM as a non-overwritable tape storage area.

In some approaches, even if the host requests writing after occurrence of an error, attempts to add data to an R tape on which the error has occurred may be prevented. Therefore, the R drive may send a request to the host to exchange the R tape, and the succeeding writing is performed on another tape. The BF drive performs writing onto a storage area other than the tape recording area prohibited to be overwritten, as noted in the CM.

If an error occurs at the time of reading of an R tape, a method similar to the case of reading with the current RABF function is applicable. In the method, because the position of data on a BF tape can be known from information about a data set (e.g., via a Data Set Information Table (DSIT)) which could be read last on an R tape and information in the CM, the data is read from the BF tape.

In the description of the first and second embodiments, the configuration with one host and two drives has been described for simplification. However, the number of hosts and the number of drives are not limited thereto. Multiple hosts and multiple drives may be present, e.g., as discussed below.

A third embodiment shows a configuration in which one R drive corresponds to each of two hosts, and one BF drive is shared. FIG. 7 shows the third embodiment in which two hosts HOST 1, HOST 2, and three drives R DRIVE 1, R DRIVE 2, BF DRIVE exist. In this case, the one BF drive plays a role of a cache for the two R drives. The writing process flow, the reading method and the process performed at the time of a writing error are the same as those of the first embodiment. However, one BF drive is shared by two R drives. The BF drive may be included to distinguish data to be recorded onto a BF tape, either for the R drives 1 or 2, before executing BFWrite.

For example, as described below, a determination can be made as to which of the R drives 1 or 2 data temporarily recorded on a BF tape is for. A determination is made as to which of the R drives the last data, among multiple data clusters included in a data set recorded on a BF tape, is for. Therefore, an identity of the R drives 1 and 2 that the last data corresponds to is stored in the DSIT. More specifically, for the last data included in each of the data sets (DS, DS+1, DS+2, etc.) on the tracks of a BF tape based on the RABF technique in the writing process <4> of the first embodiment as depicted in FIG. 3, a determination may be made as to whether the data is for the R drive 1 or 2 by the DSIT of each data set.

A fourth embodiment is a tape recording system capable of switching multiple tape drives among the works of a BF drive, an R drive and a regular drive according to various situations. For example, in a tape recording library having multiple drives, other drives which are not used can be effectively utilized as BF drives.

According to one embodiment, in a tape library (library tape storage system) including the multiple tape drives, there may be little or no difference among the BF drive, the R drive and the regular drive, from the viewpoint of hardware. If the operation of the multiple various kinds of tape drives included in the tape recording system can be changed according to the conditions at the time, the system operability of the tape library is improved.

FIG. 8 shows an example of a procedure 800 for a tape drive to switch among the works of a BF drive, an R drive and an regular drive functioning alone according to situations. The procedure 800, in some approaches, may be performed in any desired environment, and may include embodiments and/or approaches described in relation to FIGS. 1-7. Of course, more or less operations than those shown in FIG. 8 may be performed as would be known to one of skill in the art upon reading the present disclosure.

A tape drive (drive A) in a library receives writing (Write) and synchronization (Flush) requests from the host in operation 802. The drive A operates as a regular drive and writes data to a tape by the RABF function in operation 804. In operation 804, the drive A searches for a tape drive which is not used by the host (an empty drive) from drives in the library in operation 806. Upon deciding whether or not an empty drive is found in operation 808, if an empty drive is not found, the writing cycle by the RABF function is continued in operation 810. However, if an empty drive (drive B) is found, the drive A causes the drive B to be in a reserved state in operation 812.

A BF tape cartridge is mounted and the drive B prepares for BFWrite by returning a response to the effect that it is reserved (Reservation Conflict) when receiving a use request in operation 814. When the writing by the RABF function started at operation 804 is paused, the drive A ends continuation of the RABF cycle in operation 816.

Finally, the writing process according to the embodiments described above (for example, the first embodiment) is started in operation 818. The drive A functions as an R drive and uses the drive B as a BF drive. After that, this tape library executes a writing process similar to the first embodiment (the method in which an R drives is directly connected to a host). By using the above procedure, it is possible to apply the writing method in an existing tape library without newly adding a drive.

The embodiments have been described with regard to a tape drive. However, the contents of the present embodiments are not limited thereto. The host (upper apparatus) is not limited to a host computer such as a server, but may include an embodiment in which a data storage apparatus is an upper apparatus. In a further embodiment, the tape recording system may be a lower apparatus. According to the tape recording system shown above which includes at least two or more tape drives, there is obtained an advantage that, irrespective of frequent synchronization requests, it is possible to maintain tape recording density without deteriorating data writing performance.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents. 

1. A tape storage system, comprising: two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, wherein a first of the tape storage apparatuses is configured to receive multiple data clusters and a synchronization request from a host, and, when one of the segments of the buffer is accumulated and filled with the data, to write the accumulated data onto a tape, and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and the second tape storage apparatus being configured to write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.
 2. The tape storage system according to claim 1, wherein the first tape storage apparatus does not write data in the buffer until at least one segment of the buffer is completely accumulated with data, ignoring the synchronization request corresponding to the data; and when the predetermined number of data accumulated in the segments is to be dumped onto a tape at the timing corresponding to the synchronization request, the second tape storage apparatus pads an area of the segments which is unfilled with the data, to write out the data of the segments.
 3. The tape storage system according to claim 2, wherein the tape on which writing has been performed by the first tape storage apparatus is treated as a regular writing tape to which data accumulated in the segments are written as data sets; and on the second tape on which writing has been performed by the second tape storage apparatus, data accumulated in the segments are written as data sets, and the interval between the data sets on the second tape reflects the time interval of the synchronization request.
 4. The tape storage system according to claim 3, wherein the second tape storage apparatus is able to continuously and overwritably use an area of the second tape storing data already written by the first tape storage apparatus.
 5. The tape storage system according to claim 4, wherein, if a data writing error occurs in the first tape storage apparatus, and the data has already been written by the second tape storage apparatus, the data writing error is not reported to the host.
 6. The tape storage system according to claim 4, wherein, if a data writing error occurs in the second tape storage apparatus, and the data has already been written by the first tape storage apparatus, the data writing error is not reported to the host.
 7. The tape storage system according to claim 6, wherein, if the data writing error occurs in the second tape storage apparatus, the data corresponding to the error is written again into an unused tape area which includes a tape storage area of the second tape that stores data already written in the first tape storage apparatus.
 8. The tape storage system according to claim 5, wherein, if the data writing error occurs in the first tape storage apparatus, the data is written from the second tape in the second tape storage apparatus to restore data at an error position of the tape in the first tape storage apparatus via an inter-drive communication connection.
 9. The tape storage system according to claim 8, wherein the first tape storage apparatus is configured to communicate with the host via Fibre Channel or SCSI, and the inter-drive communication connection between the two tape storage apparatuses is an Ethernet connection.
 10. The tape storage system according to claim 1, further comprising the host.
 11. A tape storage system, comprising: two or more tape storage apparatuses each having a buffer divided in fixed-length segments, and being connectable to a host, a first of the tape storage apparatuses being configured to receive multiple data clusters and a synchronization request sent from a host, and being configured to write a predetermined number of data clusters accumulated in the segments onto a tape at a timing corresponding to the synchronization request, and wherein a second of the tape storage apparatuses is connected to the first tape storage apparatus, the second tape storage apparatus being configured to receive the multiple data clusters sent from the host via the first tape storage apparatus, and, when the segment thereof is accumulated and filled with the data, writing the accumulated data onto a second tape.
 12. The tape storage system according to claim 1 wherein the first tape storage apparatus does not write data in the buffer until at least one segment of the buffer is completely accumulated with data, ignoring the synchronization request corresponding to the data; and when the predetermined number of data accumulated in the segments is to be dumped onto a tape at the timing corresponding to the synchronization request, the second tape storage apparatus pads an area of the segments which is unfilled with the data, to write out the data of the segments.
 13. The tape storage system according to claim 11, wherein the tape on which writing has been performed by the first tape storage apparatus is treated as a regular writing tape to which data accumulated in the segments are written as data sets; and on the second tape on which writing has been performed by the second tape storage apparatus, data accumulated in the segments are written as data sets, and the interval between the data sets on the second tape reflects the time interval of the synchronization request.
 14. The tape storage system according to claim 13, wherein the second tape storage apparatus is able to continuously and overwritably use an area of the second tape storing data already written by the first tape storage apparatus.
 15. The tape storage system according to claim 11, further comprising the host.
 16. A method, comprising: in a first tape storage apparatus having a buffer divided in fixed-length segments, receiving multiple data clusters and a synchronization request, and, when one of the segments of the buffer is accumulated and filled with the data, writing the accumulated data onto a tape; and in a second tape storage apparatus having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, receiving the multiple data clusters via the first tape storage apparatus, and writing a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request.
 17. The method according to claim 16, wherein the first tape storage apparatus does not write data in the buffer until at least one segment of the buffer is completely accumulated with data, ignoring the synchronization request corresponding to the data; and when the predetermined number of data accumulated in the segments is to be dumped onto a tape at the timing corresponding to the synchronization request, the second tape storage apparatus pads an area of the segments which is unfilled with the data, to write out the data of the segments.
 18. The method according to claim 16, wherein the tape on which writing has been performed by the first tape storage apparatus is treated as a regular writing tape to which data accumulated in the segments are written as data sets; and on the second tape on which writing has been performed by the second tape storage apparatus, data accumulated in the segments are written as data sets, and the interval between the data sets on the second tape reflects the time interval of the synchronization request.
 19. A computer program product, comprising: a computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to cause a first tape storage apparatus having a buffer divided in fixed-length segments to receive multiple data clusters and a synchronization request, and, when one of the segments of the buffer is accumulated and filled with the data, write the accumulated data onto a tape; and computer readable program code configured to cause a second tape storage apparatus, having a buffer divided in fixed-length segments and connected to the first tape storage apparatus, to receive the multiple data clusters via the first tape storage apparatus, and write a predetermined number of data clusters accumulated in the segments thereof onto a second tape at a timing corresponding to the synchronization request. 